The Denver Post apologized as well, saying on Twitter that Frei's words do "not reflect the standards and values of our organization."

Late Monday morning, the Post sent a statement to 9NEWS, which said Terry Frei was no longer with The Denver Post.

The newspaper's statement read in its entirety:

"We apologize for the disrespectful and unacceptable tweet that was sent by one of our reporters. Terry Frei is no longer an employee of The Denver Post. It's our policy not to comment further on personnel issues.

The tweet doesn't represent what we believe nor what we stand for. We hope you will accept our profound apologies."

The Post would not elaborate on whether Frei was fired or quit.

"I should have known better and I regret it," Frei said of his now-deleted tweet in a lengthier post apologizing to the Denver Post and to Indy 500 winner Takuma Sato. "I made a stupid reference, during an emotional weekend, to one of the nations that we fought in World War II."

On Sunday, Sato became the first driver from an Asian nation to win the Indianapolis 500 race, tweeting, "thank you everyone for many messages! Can't thank enough the support I've got. Great team effort."

In his apology message, Frei went on to point out that his father flew recon missions over Japan during World War II in a plane with no mounted guns. Around the time he posted the racially-charged tweet, Frei says he was on his way to visit his father's grave at Fort Logan National Cemetery.

Frei's apology may be undercut by his Twitter activity since posting it. He thanked a woman who remarked in a sympathetic tweet that Frei saw Sato's win "as incongruous with today."